Attempts have been made to give natural irregular color tones as can be seen in wool and hemp to synthetic fiber fabrics, or to obtain new visual effects by coloring fine color dots. For example, the following means are available.
(1) Yarns dyed in different colors are woven together to form a fabric.
(2) Fibers having different dyeing properties are woven together to form a fabric, and the fabric is dyed.
(3) Spot patterns, as many as the number of colors, are printed by roller printing or screen printing, etc.
(4) Particles containing dyes are applied to a fabric for coloring.
(5) Fibers with structural variations are dyed.
Of these means, those which can express natural color shade variations called a grandrelle tone or sprinkly colored tone are mainly (3) and (5), but (3) has a problem that it involves trouble and cost for engraving the roll or manufacturing the screen printing plate. On the other hand, if fibers, for example, having thickness variations as structural variations of (5) are dyed by any ordinary method, thick portions are dyed darkly while thin portions are dyed lightly. So, (5) is said to be promising as a means for expressing a grandrelle tone since a natural irregular color tone can be given.
Synthetic fibers having thickness variations in the longitudinal direction of the fibers include polyester fibers, polyamide fibers, etc. Methods for producing polyester fibers are proposed in Japanese Patent Laid-Open (Kokai) Nos. 52-103523, 55-16930, etc. Methods for producing polyamide fibers are proposed in Registration No. 2572035, Japanese Patent Laid-Open (Kokai) No. 63-211335, etc.
These fibers can be dyed to have color shade variations. However, polyamide fibers cannot clearly manifest color shade variations, and compared to ordinary polyamide fibers, they have a problem of declining in wash fastness. That is, when a polyamide fabric having fiber thickness variations is dyed, an acid dye generally used for any ordinary polyamide fabric is used. However, when polyamide is dyed by an acid dye, the dye migrates, making it difficult to clearly express the so-called grandrelle tone peculiar to fibers having thickness variations. Furthermore, if fibers with such structural variations are dyed by an acid dye, the wash fastness of the dyed fabric declines. So, to keep fastness, the crystallinity must be intentionally raised, which lessens the structural variations.
To improve the grandrelle tone, the color shade variations can be intensified by increasing the sectional area ratio of thick portions to thin portions, but the dyed product obtained has deep dyed stripes and cannot have a high grade grandrelle tone. Furthermore, the dyed product obtained by using a fabric intensified in fiber thickness variations declines further in wash fastness disadvantageously.
Against this technical background, a dyeing technique to assure an intensive grandrelle tone and excellent wash fastness is being demanded.
Furthermore, the inventors found that for dyeing a polyamide fabric having fiber thickness variations in a grandrelle tone, if the premetalized dye has poor dye leveling property compared to an acid dye, the grandrelle tone can be intensified to some extent while wash fastness can also be improved. However, the grade of the grandrelle tone is poor, and the premetalized dye is dark in hue and cannot express a clear color.
On the other hand, it is publicly known that a reactive dye can dye an ordinary polyamide fabric. For example, Japanese Patent Laid-Open (Kokai) No. 7-97777 discloses a method of dyeing polyamide fibers by a reactive dye in an acid to neutral bath. However, practically, polyamide fibers dyed by a reactive dye have often irregular stripes, etc. disadvantageously, and a reactive dye is not practically applied since the application of a reactive dye for polyamide fibers has no advantage compared to the use of a conventional acid dye free from the problem. In this situation, it is not known at all that a grandrelle tone with clear color shade variations can be obtained by dyeing a polyamide fabric with structural variations in the longitudinal directions of the fibers using an anionic reactive dye.